perf(stark): fuse deep-composition reconstruction for both FRI points#775
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Oppen wants to merge 3 commits into
Open
perf(stark): fuse deep-composition reconstruction for both FRI points#775Oppen wants to merge 3 commits into
Oppen wants to merge 3 commits into
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Reconstructing the deep composition polynomial per query walked the OOD table, the trace-term coefficients, and inverted the trace/comp denominators independently for the regular and symmetric evaluation points, even though the OOD-derived terms don't depend on the point. Rewriting coeff*(base-ood)*denom as denom*(coeff*base - coeff*ood) isolates the point-independent coeff*ood term (computed once, shared between both points) from coeff*base (cheap base*ext multiply for base-field columns), and lets both denom sets batch-invert together. Multi-query recursion profile: 2,210,366,539 -> 1,951,764,531 cycles (-11.7%); step 3 (FRI) 912M -> 652M cycles (-28.5%).
The doc comment on reconstruct_deep_composition_poly_evaluation_pair restated the inline comment three lines into the function body.
reconstruct_deep_composition_poly_evaluation_pair walked the z*g^k
ladder twice per query (once per evaluation point) though it doesn't
depend on which point is being evaluated; interleave the two
denominator pushes into one walk instead. The 2-element composition-
tail batch inverse also went through the general Vec-allocating
inplace_batch_inverse; hand-roll it (one inversion, three muls, no
allocation).
Also mark the IsSubFieldOf<Degree{2,3}GoldilocksExtensionField> mul/
add/sub impls for GoldilocksField #[inline(always)], matching the
sibling IsField impls on the same types — these are exactly the cheap
asymmetric ops the deep-composition reconstruction fusion relies on.
Multi-query recursion profile (two make-rebuilt runs per side, since
the underlying proof has run-to-run variance): baseline 1,947,221,680
/ 1,947,263,739 cycles; with this change 1,939,869,854 / 1,939,845,966
(-~7.37M, -0.38%). No correctness change (in-VM verify output digest
identical to the prior commit).
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Summary
reconstruct_deep_composition_poly_evaluation(STARK verifier, FRI step)into one traversal, sharing the OOD-table walk, the
trace_term_coeffswalk, and both
inplace_batch_inversecalls per query. The core trick:coeff*(base-ood)*denomdistributes to
denom*(coeff*base - coeff*ood), isolating thepoint-independent
coeff*oodterm (computed once, shared between bothpoints) and letting base-field columns use the cheap
IsSubFieldOfasymmetric multiply instead of a full extension-field product.
z*g^kladder walk within a query (was computedtwice, once per evaluation point), hand-rolls the 2-element
composition-tail batch inverse to avoid a Vec allocation, and marks the
IsSubFieldOf<Degree{2,3}GoldilocksExtensionField>mul/add/sub impls#[inline(always)]to match their siblingIsFieldimpls.Measured impact
Multi-query recursion profile (
make test-profile-recursion-multi; theunderlying proof has ~40-45K cycles of run-to-run variance from
stark::grinding::generate_nonce's parallelfind_anysearch, so alldeltas below are 2-sample-cluster-to-cluster, not point-to-point):
85fa5b3e): ~1,947,242,710 cycles (-11.9%)3ac5e494): ~1,939,857,910 cycles(a further -0.38%, -14.2% total from baseline)
Single-query and step-3 (FRI) improvements are proportionally similar; see
individual commit messages for per-commit numbers.
Soundness
Every guard the two-call version had (base/aux-length checks, the
trace_term_coeffssanity check, batch-inverse zero-rejection, thecomposition-poly-parts-count check) is reproduced exactly or made strictly
stricter in the fused version — verified by independent adversarial review
agents against the reject-path semantics, the algebraic identity, and the
soundness threat model (a dishonest prover cannot craft a proof this code
accepts that the prior code would have rejected).
Test plan
make test(workspace-wide; only failure ismath-cuda, which needsa GPU unavailable in this environment — pre-existing, unrelated)
make test-ethrexcargo test -p lambda-vm-prover --lib test_recursion_execute_1query -- --ignored --nocapture(in-VM end-to-end verify, output digestunchanged across all three commits)
then a second round covering performance/simplicity) on the diff